Liquid cooled exhaust manifolds are used in association with internal combustion engines, particularly for marine applications. In marine applications, it is desirable to limit the temperature of an exhaust manifold and associated exhaust pipes. Because the engines are commonly enclosed in relatively tight engine compartments, it is necessary to cool the exhaust manifolds of the marine engine with a liquid coolant.
A modern, liquid cooled exhaust manifold typically has a configuration similar to the subject exhaust manifold. Specifically, a manifold housing has exhaust gas conduit portions, one for each of the cylinders in a bank of the engine. For example, a V-8 engine utilizes two liquid cooled exhaust manifolds, each having exhaust conduits adapted to carry away the exhaust products of each cylinder for each bank of the engine. It is desirable to provide a high point in the exhaust system above the water line of a boat to prevent any siphonic action. A typical exhaust gas outlet is located high and the inlet apertures are located low on the manifold. The exhaust gases flow upward from the inlets through individual gas passages in the manifold and are connected to a common passage. The common passage is connected to the outlet aperture usually located at the top of the manifold. These upwardly extending exhaust passages for each cylinder extend generally in side-by-side relationship to one another and also are spaced apart corresponding to the exhaust port spacing. The individual exhaust gas passages must also be spaced to provide open spaces or access windows therebetween so that the engine spark plugs can be reached.
Typical exhaust manifolds are cooled by the passage of a liquid coolant such as water which flows through spaces or coolant jackets surrounding the exhaust gas passages. Specifically, the exhaust manifold is a cast structure with a double wall construction, the inner wall of which defines the individual exhaust gas passages and the common exhaust or collector passage. The outer walls of the exhaust manifold define the coolant space or jacket about the inner wall so that liquid coolant can be pumped through the exhaust manifold and about the exhaust carrying passages. This cooling arrangement limits the temperature of the outer wall and permits the engine and manifold to be used in a marine application where high temperatures are undesirable.